1. Field of the Invention
The present invention relates to encapsulated oil-in-water type emulsion compositions.
2. Discussion of the Background
In the cosmetic field, oil-in-water type emulsions that provide a moisturizing feeling to the skin during use and impart a non-oily feeling have been widely used. However, such emulsions are generally thermodynamically unstable, and have a characteristic that they result in creaming due to a difference in the specific gravity between an oil and water, aggregation caused by collision between particles, and separation into two phases in the end caused by coalescence of the dispersed phase. Accordingly, various trials have been made so far in order to prevent such coalescence of the dispersed phase.
Several attempts to stabilize such emulsions were made by adding a third component. By increasing the amount of an emulsifying agent, an attempt to stabilize such an emulsion was made (see, Contact Dermatitis, vol. 33, 4, p. 217 (1955)), however, not only was the prevention of coalescence incomplete, but also a problem arose that a sticky feeling unique to an emulsion was conspicuous.
Further, an attempt to obtain a stabilized emulsion was also made by using a water-soluble thickening agent such as an alkyl-modified carboxyvinyl polymer (see, JP-A-7-149621). However, it did not achieve the prevention of coalescence.
Further, an approach in which a solid or semi-solid oil, a water-soluble thickening agent, an oil-soluble thickening agent are combined was also made (see, JP-A-6-157240). However, a problem in stability arose; a sticky feeling derived from the solid or semi-solid oil component or a slimy feeling derived from the water-soluble thickening agent was caused; it was not a widely-used technique, because an extremely special equipment was required for the production, and so on, and any of the oil-in-water type emulsion compositions were not satisfactory.
On the other hand, an attempt to improve a technique of emulsification was also made. An attempt to form an emulsion particle into a fine particle with a size of 0.3 micrometer or less by carrying out an emulsification treatment under a high pressure of 1000 psi or more was made (see, JP-A-10-259114). However, the softening temperature of the entire oil phase was 50° C. or below, and therefore, the stability thereof at a high temperature was low, and it was not always satisfactory.
Further, several attempts to achieve encapsulation thereof were made actively. Thus, an attempt to utilize the characteristic of an aqueous cosmetic, while preventing the coalescence of the oil phase by a capsule film composed of calcium alginate, was made (see, JP-A-2-117610). However, in such an alginate capsule, the raw material to be blended was limited, it could only be used in a specific pH range, the viscosity was decreased by a polyvalent metal ion used in a curing reaction in the case where an outer phase with low salt resistance was used, and so on, and it was not always satisfactory.
An attempt to achieve stabilization by a soft capsule containing an agar as a base was made (see, JP-A-1-193216). However, when it was applied to the skin as a cosmetic, there was an undeniable sense of a foreign matter that agar debris remained on the skin.
Thus, there remains a need for an encapsulated oil-in-water type emulsion composition in which coalescence of the dispersed phase does not occur, and which can be produced by a simple method without resort to a special apparatus, is excellent in stability with time, does not impart an uncomfortable feeling during application, is excellent in a sensory feeling that satisfies both of a moisturizing feel and an emollient feel and is excellent in appearance.